The issue

First stable release of PHP version 5 was done two years ago. This
version of language has matured a lot throughout these two years and with
PHP version 4 development effectively stopped should already be considered
the preferred platform by developers of new PHP libraries and
applications.

PEAR policies encourage "backwards compatibility", which
unfortunately means supporting the inadequate object model of PHP version
4. While it does make sense for existing packages, requiring such
"backwards compatibility" for new packages that get accepted into PEAR has
at least two problems:

It slows the adoption of PHP version 5 by users of PEAR

PEAR risks becoming a garbage dump of obsolescent code, or at
least be perceived as one